To avoid drowsy operation by the operator of an automatic device or the like, it has been studied to measure the heartbeat of the operator and detect the drowsiness or arousal level of the operator on the basis of the measured heartbeat (e.g., Japanese Laid-open Patent Publication No. 2009-142576).
In a vehicle, for example, electrodes are provided in the steering wheel or any other location to be brought into contact with the driver. When the driver touches the electrodes, an electrocardiographic signal of the driver may be detected. The detected electrocardiographic signal is subjected to noise reduction processing or other signal processing. The heartbeat of the driver may be measured by, for example, analyzing the heartbeat signal called the R wave included in the electrocardiographic signal subjected to signal processing.
A heartbeat signal detected by electrodes includes a lot of noise signals. It is difficult to measure accurately the heartbeat of the driver unless the noise signals detected together with the heartbeat signal are appropriately processed.